Rigid urethane foams can be produced in situ using spray means or the like and have been used in various fields including building field as an heat-insulating material for preventing dew condensation or the like. However, such urethane foams have a drawback of low flame retardancy. In this situation, phenolic resin foams have come into use, the foams being superior not only in flame retardancy but in heat insulation property, sound insulation property and the like. However, the phenolic resin is difficult to spray in an evenly dispersed state due to its high viscosity, and at a low temperature, the foaming reaction is hindered, giving a foam which is brittle at the surface and low in adhesion. In short, difficulties are encountered in in situ production.
Generally a phenolic resin foam is prepared as follows. A resol phenolic resin serving as a raw material is mixed with a blowing agent, a foam stabilizer, a curing agent and other additives to give a uniform composition. Then the composition is poured into a mold and expanded at an elevated temperature.
In said production of phenolic resin foams, chlorofluorocarbons are used as a low-boiling organic compound-based blowing agent, said chlorofluorocarbons having a low heat conductivity and showing high heat insulation property when enclosed with closed cells. For example, trichlorofluoromethane (CFC-11) and trichlorotrifluoroethane (CFC-113) have been chiefly used.
In recent years, however, it has been suggested that some chlorofluorocarbons, when released into the atmosphere, would deplete the stratospheric ozone layer, and would cause global warming due to greenhouse effect, thereby inflicting a serious adverse influence on the ecosystem including humans. An international agreement calls for a restriction of use of chlorofluorocarbons involving a high ozone-depleting risk. Said CFC-11 and CFC-113 are among the chlorofluorocarbons to be controlled for restriction. From this viewpoint as well, there is a need for development of novel blowing agents which are free from the ozone-depleting and global warming problems or substantially without such risks.
Of late, it was proposed to use 1,1-dichloro-1-fluoroethane and 1,1-dichloro-2,2,2-trifluoroethane as chlorofluorocarbons which would exert little influence on the ozone layer, and they have currently come into use. Yet these chlorofluorocarbons threaten us with ozone depletion none the less because they contain chlorine in the molecule. Japanese Unexamined Patent Publications Nos. Hei 2-29440 and Hei 2-235982 proposed to use chlorine-free fluorohydrocarbons free from ozone-depleting risks. Japanese Unexamined Patent Publication No. Hei 5-239251 proposed the use of 1,1,1,3,3-pentafluoropropane as a blowing agent for the production of plastic foams.
1,1,1,3,3-pentafluoropropane (HFC-245fa) which is a non-inflammable compound with a boiling point of 15.degree. C. and a hydrogen-containing fluorohydrocarbon is considered to entail little or no ozone-depleting or global warming risks.
Currently attention is directed to 1,1,1,3,3-pentafluoropropane as a promising candidate substitute for CFC-11 and CFC-113 because of its boiling point close to theirs and its non-inflammability.